Low temperature process for the recovery of ethane from a stripped natural gas stream



Dec. 26, 1967 R. N. D] NAPOLI LOW TEMPERATURE PROCESS FOR THE RECOVERY OF ETHANE FROM A STRIPPED NATURAL GAS STREAM Filed April 29, 1966 w W m m a h I .M 0 N w o- N Du mm 0 H m #& 1 1 $3528 N E T s r m 1 m w A m 1 s 3 m 1 t E g 9 Pg 2; E: W $25? a 0d a B m F8 MW r m WU NH NW l\, H Y mm vm EW WW N H B H. .J 2 a E 22 MN as a Q )I w, m? T 2 2 m N w 523% 0w f M Aki wiv M a a m. .m cm W WE m a x f I m 4 4 a n 2 m a N w a Q s m 7 J K a 1: 0 d 13 k f O m a h m N NR w 2 w H6 2 v NM w a a a P w 0 a w $2528 "D a 2 United States Patent 3,359,743 LOW TEMPERATURE PROCESS FOR THE RE- COVERY 0F ETHANE FROM A STRIPPED NATURAL GAS STREAM Robert N. Di Napoli, North Bellmore, N.Y., assignor to National Distillers and Chemical Corporation, New York, N .Y., a corporation of Virginia Filed Apr. 29, 1966, Ser. No. 546,398 21 Claims. (Cl. 6228) The present invention relates to an economical process for the recovery of ethane and heavier components from a stripped or lean natural gas stream.

The natural gas streams from which ethane and heavier hydrocarbons are recovered in accordance with the invention in most instances have been stripped of propane and heavier components and a large portion of ethane in a lean oil absorption plant. The recovery of additional, worthwhile amounts of C hydrocarbons from such streams has previously been considered to be uneconomical.

Known techniques for removing C hydrocarbons from natural gas streams have frequently involved processing at reduced temperatures and pressures which result in the condensation of a substantial amount of methane as a liquid. Such processes also commonly result in a large decrease in pressure of the gas stream during processing so that a great deal of energy is required to return the tail gas at pipeline pressure.

Therefore, the primary object of the present invention is to provide an improved method for efliciently recovering C hydrocarbons from a stripped or lean natural gas stream. A further objective is to accomplish this recovery with a minimum requirement of external power for compression or refrigeration. An additional object is to recover C hydrocarbons from a natural gas stream without substantial condensation of methane. An additional object is to recover C hydrocarbons from a lean gas feed by a method which minimizes the pressure differential between the feed gas and the tail gas.

In accordance with the present process, it has been found that ethane and heavier components may be economically recovered from a lean natural gas stream by a process which generally comprises:

(a) Providing a lean natural gas feed at a pressure in excess of about 450 p.s.i.a., and preferably in the range of from 450 to 800 p.s.i.a.,

(b) Pre-cooling the feed to a temperature, generally on the order of from 75 to --110" R, such that on subsequent expansion, the temperature is reduced to a level at or near the hydrocarbon dew point of the gas,

(0) Expanding the feed gas as described in (b), preferably by passing it through an expander such as an expansion turbine or an expansion engine to reduce the temperature to a value in the range of from about -90 to 125 F. and to reduce the pressure to a value above about 400 p.s.i.a., and preferably in the range of from 400 to 600 p.s.i.a.,

(d) Cooling the incoming gas stream by (1) indirect heat exchange with tail gas and the liquid C hydrocarbons condensate stream and (2) further expansion to form a liquid condensate rich in ethane and heavier components,

(e) Separating the liquid condensate from the vapor fraction, preferably by flashing into a suitable separation chamber, and

(f) Rectifying the vapor fraction obtained in step (e) to recover additional ethane and heavier components in liquid form.

The liquid condensate from steps (e) and (f) is then preferably used for heat exchange in the cooling step (d) and is de-methanized. The vapor fraction, remaining after rectification for ethane recovery and primarily containing methane, is joined with de-methanized overhead vapors and is also preferably recycled for indirect heat exchange with the incoming gas stream in step (d) and (b) to effect cooling of the gas prior to the condensation stage.

In one variation of the process, the lean natural gas feed first may be enriched by transferring a C hydrocarbons fraction from one or more other natural gas streams to the feed stream. The manner in which enrichment of the feed is accomplished is described more fully below. Ordinarily, lean natural gas streams have a C content on the order of about 3.5 mol percent. The present process is highly eflicient in the recovery of the C fraction from such gas streams, whether or not they have been enriched as described below.

More specifically, in accordance with the invention, a lean natural gas feed is provided under a pressure in excess of 450 p.s.i.a. and preferably in the range of from 450 to 800 p.s.i.a., and at a temperature near ambient. The gas feed is then pre-cooled, preferably by indirect heat exchange with effiuent tail gas, and then is preferably passed through a battery of fixed bed driers to dry the gas composition. It will be understood that the temperatures stated in the present specification are illustrative for a specific gas feed and may vary considerably depending upon the composition of the gas stream.

The gas stream is then further pre-cooled by indirect heat exchange with efiluent tail gas and the (3 hydrocarbons product stream to reduce the temperature of the feed into the range of from to F.

The gas feed is then expanded through an expander to reduce the pressure to above about 400 p.s.i.a. and preferably in the range of from 400 to 600 p.s.i.a. The expansion brings about a reduction in the temperature of the gas stream to a value in the range of from 90 to F.

The temperature at the inlet to the expander is adjusted such that the discharge temperature is a few degrees above the hydrocarbon dew point temperature, thus avoiding the formation of liquid in the expander. The fact that the composition of the gas is high in methane and low in ethane and heavier components permits expansion of the gas to a relatively low temperature without condensation of liquid. The reduction in the temperature difference between the cooling feed gas stream and the warming tail gas stream which normally occurs near the dew point of the feed gas is thus avoided by expansion of the gas at this point, thereby eliminating the need for suppplemental refrigeration at this point in the process. The work derived from the expansion is recovered and used to offset the refrigeration and recompressi-on utility requirements of the system.

The gas is then further cooled by indirect heat exchange with the effluent tail gas and hydrocarbon condensate streams. In this manner, the gas is additionally cooled to a temperature in the range of from 100 to F.

The feed is then again expanded, preferably by a pressure letdown through a throttling valve, to yield a liquid condensate phase containing nearly 70% of the ethane contained in the original feed gas.

The liquid condensate-vapor mixture is then separated. This is preferably accomplished by flashing into a separator drum from which the liquid condensate is withdrawn and the vapors are flashed overhead.

The vapor fraction from the separator is passed to a rectification column where additional liquid C hydrocarbons are recovered. This material is combined with the liquid withdrawn from the separator, providing :a total yield of about 90% of the 0 hydrocarbons content of the feed.

The combined liquid condensate streams withdrawn from the separator drum and recovered by rectification are partially vaporized by heat exchange with the feed gas and are then introduced into a denethanizing tower. In the tower, overhead vapors are removed and combined with the tail gas from the rectification column, are recycled for heat exchange cooling of the feed gas and are then recompressed and returned to the pipeline.

The de-rnethanized liquid ethane and heavier fraction is then recycled in heat exchange with the feed gas which vaporizes the condensate so that the product C hydrocarbons may be withdrawn as a gas.

If desired, the initial lean gas stream may be enriched by the transfer of ethane and/or heavier hydrocarbons from one or more independent natural gas streams. Ethane and/or heavier hydrocarbons are recovered from such gas streams by compressing and cooling the gas stream to condense a (3 fraction, heat exchanging the condensed fraction with the incoming gas to recover a portion of the refrigeration requirements and to re-vaporize the fraction and then combining the re-vaporized fraction with the lean gas stream to provide an enriched feed.

The invention will be more fully appreciated in the light of the following detailed example considered with reference to the accompanying drawing.

The single figure of the drawing is a fiow diagram of a preferred embodiment of the process as illustratively described in connection with the example set forth below.

Example A stream of lean natural gas is introduced into the system at a pressure of 610 p.s.i.a. and a temperature of 100 F. The gas feed has the following approximate composition:

Mol percent The feed stream may also contain some carbon dioxide. Depending on its concentration, the feed gas may be pretreated by known techniques to remove carbon dioxide or reduce the content below contaminating levels. Feed gas containing concentrations of carbon dioxide in the range of 1 mole percent may be processed without treatment. In this case, the major portion of carbon dioxide will concentrate in the C hydrocarbons product stream.

The feed gas is introduced through conduit 1 and is split into two streams in conduits 2 and 3. Streams 2 and 3 are passed through pre-coolers 4 and 5 respectively, reducing the temperature of the gas to about 50 F. During the pre-cooling, the gas streams are withdrawn from pre-coolers 4 and 5 through conduits 6 and 7 and are passed through a battery of fixed bed driers containing activated alumina absorbent for drying the gas to reduce the water vapor dew point to about -70 F. The dried gas stream is again split and returned to pre-coolers 4 and 5 where the temperature of the gas is reduced to about 50 F.

The gas cooling requirement in pre-cooler 4 is provided by efiiuent tail gas introduced through conduit 8 and withdrawn through conduit 9. The temperature of the tail gas is approximately --68 F. at the input side of the pre-cooler and approximately 83 F. on the output side.

The gas cooling requirements of pro-cooler 5 are met primarily by indirect heat exchange with the liquid hydrocarbon prod'uct stream which is recycled from the demethanizer through conduit 10 into the pre-cooler and is then withdrawn through conduit 11. The temperature of the hydrocarbon product stream on the input side of pre-cooler 5 is approximately 60 F. and the temperature on the output side is approximately 92 F.

The gas feeds from pre-coolers 4 and 5 are then combined at a temperature of about -50 F. and are introduced into chiller 12 Where the temperature of the gas is further reduced to about 86 F. The gas feed is withdrawn through conduit 13 and, at this point, due to normal pressure drop in the system, the gas is under a pressure of approximately 600 p.s.i.a.

The gas cooling requirements of chiller 12 are furnished by tail gas which is introduced through conduit 22 and withdrawn through conduit 8. Indirect heat exchange with the feed is effected in chiller 12. The temperature of the tail gas at the input side of the chiller is about l1l F. and at the output side is about -68 F.

The gas feed is then expanded through an expansion engine 14 to recover available energy which is used to offset partially the refrigeration and reoompression utility requirements. In this manner, about 15% of the process energy requirements are recovered.

The expansion results in a reduction of the temperature of the gas to about 106 F. and a reduction of the pressure to about 490 p.s.i.a. The gas feed is withdrawn from expander 14 through conduit 15 and is split into two portions in conduits 16 and 17.

The gas in conduit 16 is introduced into a partial condenser 19 and is withdrawn from the condenser 19 through conduit 20 at a temperature of approximately -124 F. The refrigeration requirements of partial condenser 19 are provided by effluent tail gas which is recycled for heat exchange in condenser 19 and is then withdrawn through conduit 22. The temperature of the effluent tail gas on the input side of condenser 19' is approximately 137 F. and on the output side is approximately l1l F. As described above, the tail gas from condenser 19 is then conducted through chiller 12 for additional heat exchange cooling of the feed gas.

The portion of the gas feed in conduit 17 is introduced into another partial condenser 23 and is withdrawn through conduit 24. The refrigeration requirements of condenser 23 are furnished by indirect heat exchange with the liquid condensate stream from separator 27 which is intro duced into condenser 23 through conduit 25 and is withdrawn from condenser 23 through conduit 26. The liquid condensate stream in conduit 25 contains C hydrocarbons and a substantial amount of methane. The temperature of this liquid on the input side of condenser 23 is about F. and on the output side is about 124 F. This increase in temperature results in about a 40% partial re-vaporization of the condensate.

The separate gas streams in conduits 20 and 24 are combined in conduit 30, flashed through valve 31 and, introduced into separator 27.

This results in a reduction of the pressure to about 465 p.s.i.a. and cooling of the feed to about l28.5 F. A liquid condensate containing substantial amounts of C hydrocarbons mixed with gas, largely methane, is withdrawn from separator 27 through conduit 18.

The overhead vapors from separator 27 are withdrawn through conduit 70 and introduced into ethane rectifier 71. In ethane rectifier 71, a (3 hydrocarbon liquid condensate is separated and withdrawn through conduit 76 at the bottom of the ethane rectifier. The overhead vapors are withdrawn through conduit 72, are cooled further in heat exchanger 73 and are then introduced into separator 74 where a heavy fraction is condensed, separated and returned to the ethane rectifier through conduit 75. The overhead vapors are then conducted through conduit 32 and are combined with those from separator 36 in conduit 21.

After heat exchange with the gas feed in condenser 23, the combined liquid condensate from the ethane rectifier, withdrawn through conduit 76, and from separator 27, withdrawn through conduit 18, are introduced through conduit 26 into de-methanizer 33. In the de-methanizer, an overhead vapor fraction, primarily comprising methane, is withdrawn through conduit 34, is cooled in heat exchanger 35 and is introduced into separator 36 where a heavy fraction is removed and returned through conduit 37 to de-methanizer 33. The vapor fraction from separator 36 is withdrawn through conduit 38 and combined with the vapors from conduit 32 in conduit 21. These combined vapors, called tail gas, are employed for heat exchange cooling in condenser 19, chiller 12 and pre-cooler 4, as previously described. They are then withdrawn from pre-cooler 4 through conduit 9 at a pressure of about 450 p.s.i.a., recompressed in compressor 41 and returned to the pipeline at 610 p.s.i.a. and approximately 100 F.

refrigerating requirements in cooler 52, and is then returned to the pipeline after recompression.

-'In the above described system, heat is removed in condensers 73 and at approximately the boiling point of ethylene at atmospheric pressure. The ethylene of the heat pump is cascaded against propane in indirect heat exchange relationship. The ethylene vapors are compressed to about 235 p.s.i.a. and are condensed in heat exchange With propane at about atmospheric pressure. The propane vapors are then compressed to approximately 135 p.s.i.a. and are condensed in de-methanizer re-boiler 39.

This is a simplified description of the operation of the ethylene-propane cascade system which involves other intermediate stages, not described in detail.

The refrigeration requirements of condenser 73 used to condense C hydrocarbons from overhead vapors from rectifier 71 is justified'by a resulting increase in product yield. At separator 27, approximately 6570% of MATERIALS BALANCE TABLE The liquid (3+, hydrocarbon fraction collected in the bottom of demethanizer 33 is warmed in re-boiler unit 39 and is then Withdrawn through conduit 10 for heat exchange cooling in pro-cooler 5.

Before being introduced into pre-cooler 5, the liquid hydrocarbon product stream in conduit 10 is passed through valve 40 where the pressure is flashed down to about 58 p.s.i.a. The temperature of the liquid product stream at that point is about 60 F. Upon withdrawal from pre-cooler 5 through conduit 11, the temperature of the stream is approximately 92 F. and the products are entirely in the vapor state.

The system described may, for example, be operated with an input of about 909.6MM s.c.f.d., or about 1,000,- 000 mols per hour. On such a basis, the Cgj+ product stream Will comprise about 25.5MM s.c.f.d. or about 89,780 pounds per hour.

On such a basis, at major points in the process, indicated by letters A-I, the compositions of feed and product streams are approximately as shown in the above table.

As noted above, in one embodiment of the invention, a second gas stream in conduit is introduced into compressor 51, where it is compressed to about 645 p.s.i.a., and then into cooler 52 where it is cooled to about -85 F. C liquid fraction is condensed, separated and withdrawn through conduit 53, the liquid condensate is then returned in indirect heat exchange relationship with the input gas in cooler 52 to provide at least part of the refrigeration requirements in cooler 52 and to re-vaporize the condensate. The re-vaporized condensate is Withdrawn from cooler 52 through conduit 54 and is combined, after recompression in compressor 56, with a lean gas stream for use as a feed in conduit 1 of the system.

The vapor fraction from cooler 52 is also recycled for heat exchange with incoming gas in cooler 52, is withdrawn through conduit 55, after furnishing a part of the A B C D E F G H I Feed Gas 124 F 1 24 F Rectifier Rectifier Demethan. Demethan. Demethan. Tail Vapor, Liquid, 0vl1'd., Bottoms, Feed, Bottoms, Ovhd., Gas,

MPH M MPH MPH MPH MPH MPH MPH M.s.c.i.d. MPH- available C hydrocarbons is condensed, but by treating the overhead vapors from the separator in rectifier 71, a recovery of about 90% of the C hydrocarbons content of the feed is realized.

By comparison simple condensation of C '-|-v hydrocarbons from a lean gas stream would require condensation of 65% of the gas feed to obtain 90% recovery. By the present method, the same level of recovery is achieved with condensation of only about 33% of the gas feed.

The rectification permits 90% recovery with about 50% of the energy expenditure that wouldbe required to obtain the same level of recovery by further simple condensation.

In the process illustratively described above, using a gas feed of the indicated com-position, horsepower expended in recovering ethane and heavier components is about 0.3 HP/lb., and, in recovering ethane is about 0.4 HP/ lb.

It will also be noted that the pressure differential between the feed gas, about 610 p.s.i.a., and tail gas after heat exchange in pre-cooler 4, and 450 p.s.i.a. is limited to about p.s.i.a. Therefore, relatively little energy is required to recompress the tail gas to pipeline pressure. In general, it is a feature of the process that the diflerential between the pressure of the feed gas and the pressure of the tail gas may be kept below about 200 p.-s.i., so that recompression power requirements are minimized.

In addition, it should also be noted that the present system enables much of the refrigeration and power requirements of the ethane recovery to be met by the energy contained in the feed :gas stream. Feed gas at the pressure indicated is ordinarily available in transmission I gas pipelines.

major proportion of the C hydrocarbons content of a lean natural gas stream.

It will be apparent to those skilled in the :art that various modifications may be made in the process as described Without departing from the scope of the invention as expressed in the following claims.

What is claimed is:

1. A method for recovering a major portion of the (3 hydrocarbons content of a lean natural gas stream without substantial condensation of methane, the C hydrocarbon content being about 3.5% of the feed, comprising (a) providing a lean natural gas feed at a pressure in excess of about 450 p.s.i.a.,

(b) pre-cooling the lean natural gas feed to a temperature on the order of from 75 to "110 F.,

(c) initially expanding the lean natural gas feed to cool the lean natural gas feed to a temperature in the range of from 90 to -125 F. and to reduce the pressure of the lean natural gas. feed to above about 400 p.s.i.a.,

(d) cooling said expanded lean natural gas feed by indirect heat exchange with tail gas and the liquid C hydrocarbons condensate stream and by further expansion of said expanded lean natural gas feed to form a tail gas and a liquid condensate rich in C hydrocarbons containing the major portion of the C hydrocarbons in the feed,

(e) separating said liquid C 5. condensate from said tail gas,

(f) rectifying said tail gas for the recovery of additional (3 hydrocarbons,

(g) heat exchanging the liquid C condensate from steps (e) and (f) and said tail gas with said expanded lean natural gas feed in step (d), and

(h) recovering the C hydrocarbons as a product.

2. The method of claim 1 wherein the pressure of the lean natural gas feed in step (a) is in the range of from 450 to 800 p.s.i.a., and in step (c) is in the range of from 400 to 600 p.s.i.a.

3. The method of claim 1 wherein the pressure differential between the lean natural gas feed and tail gas is less than about 200 p.s.i.

4. The method of claim 1 further comprising demethanizing said C hydrocarbon product stream.

5. The method of claim 4 further comprising combining the methane vapors from said de-methanizing with said tail gas.

6. The method of claim 1 wherein said pre-cooling is accomplished by indirect heat exchange with said tail gas and said liquid C condensate.

7. The method of claim 6 wherein said liquid condensate is re-vaporized by said pre-cooling heat exchange.

8. The method of claim 1 comprising re-compressing said tail gas substantially to pipeline pressure.

9. The method of claim 1 further comprising drying said lean natural gas feed prior to condensation of 0 hydrocarbons.

10. The method of claim 1 further comprising enriching said lean natural gas feed by compressing and cooling a hydrocarbon gas stream to condense a liquid 0 hydrocarbons fraction, separating said liquid from the balance of said hydrocarbon gas stream, cooling said hydrocarbon gas stream and re-vaporizing said liquid (3 hydrocarbons fraction by indirect heat exchange between said liquid and said hydrocarbon gas stream, recompressing the re-vaporized (3 hydrocarbons fraction and introducing said fraction into said lean natural gas feed.

11. The method of claim 1 wherein the expansion of the lean natural gas feed in step (c) is carried out in 12. The method of claim 1 wherein said lean natural gas feed has substantially the following composition:

Percent CH About 95. C hydrocarbons About 3.5. CO; Less than about 1. N The balance.

13. A method for recovering a major portion of the 0 hydrocarbons content of a lean natural gas stream without substantial condensation of methane, the (1 hydrocarbon content being about 3.5% of the feed, comprising (a) providing a lean natural gas stream at about 600 p.s.i.a. and F.,

(b) pre-cooling the lean natural gas stream to a temperature of about 86 F. by indirect heat exchange with an efliuent tail gas and a (1 hydrocarbons product stream,

(c) initially expanding said lean natural gas feed through an expander to cool said lean natural gas feed to a temperature of about 106 F. and to reduce the pressure of the lean natural gas feed to about 490 p.s.i.a.,

(d) cooling said expanded lean natural gas feed to a temperature of about l24 F. by indirect heat exchange with efliuent tail gas and the (3 hydrocarbons condensate stream,

(e) reducing the pressure of said expanded lean natural gas feed to about 465 p.s.i.a. to reduce the temperature of the expanded lean natural gas feed to about 129 F. and to condense a liquid fraction rich in C hydrocarbons containing the major portion of the (3 hydrocarbons in the feed,

(f) separating said liquid C fraction from the effluent tail gas remainder of said feed,

(g) rectifying said tail gas for the recovery of additional C hydrocarbons,

(h) heat exchanging said liquid C fraction and said tail gas remainder with said expanded lean natural gas feed in step (d), and

(i) recovering the 0 hydrocarbons as a product.

14. The method of claim 13 wherein the pressure dilferential between the lean natural gas feed and tail gas is less than about 200 p.s.i.

15. The method of claim 13 further comprising demethanizing said C hydrocarbon product stream.

16. The method of claim 15 further comprising combining the methane vapors from said de-methanizer with said tail gas.

17. The method of claim 13 wherein said liquid 0 condensate is re-vaporized by said heat exchange.

18. The method of claim 13 comprising recompressing said tail gas substantially to pipeline pressure.

19. The method of claim 13 further comprising drying said lean natural gas feed prior to condensation of 0 hydrocarbons.

29. The method of claim 13 further comprising enrichmg said lean natural gas feed by compressing and cooling a hydrocarbon gas stream to condense a liquid 0 hydrocarbons fraction, separating said liquid from the balance of said hydrocarbon gas stream, cooling said hydrocarbon gas stream and re-vaporizing said liquid C hydrocarbons fraction by indirect heat exchange between said liquid and said hydrocarbon gas stream and ntroducing said re-vaporized 0 hydrocarbons fraction into said lean natural gas feed.

21. The method of claim 13 wherein said lean natural gas feed has substantially the following composition:

Percent CH About 95. C hydrocarbons About 3.5. CO Less than about 1. N The balance.

(References on following page) 9 10 References Cited 3,205,669 9/1965 Grossmann 6238 XR UNITED STATES PATENTS ,318,103 5/ 967 Jakob 6224 XR g; 5 3 at 1 -6 WILBUR L. BASCOMB, JR, Primary Examiner.

a 1n et .a Jakson 5 Examlner. 5/ 1965 Kuerston 6223 V. W. PRETKA, Assistant Examiner. 

1. A METHOD FOR RECOVERING A MAJOR PORTION OF THE C2+ HYDROCARBONS CONTENT OF A LEAN NATURAL GAS STREAM WITHOUT SUBSTANTIAL CONDENSATION OF METHANE, THE C2+ HYDROCARBON CONTENT BEING ABOUT 3.5% OF THE FEED, COMPRISING (A) PROVIDING A LEAN NATURAL GAS FEED AT A PRESSURE IN EXCESS OF ABOUT 450 P.S.I.A., (B) PRE-COOLING THE LEAN NATURAL GAS FEED TO A TEMPERATURE ON THE ORDER OF FROM -70* TO -110*F., (C) INITIALLY EXPANDING THE LEAN NATURAL GAS FEED TO COOL THE LEAN NATURAL GAS FEED TO A TEMPERATURE IN THE RANGE OF FROM -90* TO -125*F. AND TO REDUCE THE PRESSURE OF THE LEAN NATURAL GAS FEED TO ABOVE ABOUT 400 P.S.I.A., (D) COOLING SAID EXPANDED LEAN NATURAL GAS FEED BY INDIRECT HEAT EXCHANGE WITH TAIL GAS AND THE LIQUID C2+ HYDROCARBONS CONDENSATE STREAM AND BY FURTHER EXPANSION OF SAID EXPANDED LEAN NATURAL GAS FEED TO FORM A TAIL GAS AND A LIQUID CONDENSATE RICH IN C2+ HYDROCARBONS CONTAINING THE MAJOR PROTION OF THE C2+ HYDROCARBONS IN THE FEED, (E) SEPARATING SAID LIQUID C2+ CONDENSATE FROM SAID TAIL GAS, (F) RECTIFYING SAID TAIL GAS FOR THE RECOVERY OF ADDITIONAL C2+ HYDROCARBONS, (G) HEAT EXCHANGING THE LIQUID C2+ CONDENSATE FROM STEPS (E) AND (F) AND SAID TAIL GAS WITH SAID EXPANDED LEAN NATURAL GAS FEED IN STEP (D), AND (H) RECOVERING THE C2+ HYDROCARBONS AS A PRODUCT. 